Deuss Felix A, Gully Benjamin S, Rossjohn Jamie, Berry Richard
From the Infection and Immunity Program, Biomedicine Discovery Institute and.
the Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
J Biol Chem. 2017 Jul 7;292(27):11413-11422. doi: 10.1074/jbc.M117.786483. Epub 2017 May 17.
T cell immunoglobulin and ITIM domain (TIGIT) is an inhibitory receptor expressed on the surface of natural killer (NK) cells. TIGIT recognizes nectin and nectin-like adhesion molecules and thus plays a critical role in the innate immune response to malignant transformation. Although the TIGIT nectin-like protein-5 (necl-5) interaction is well understood, how TIGIT engages nectin-2, a receptor that is broadly over-expressed in breast and ovarian cancer, remains unknown. Here, we show that TIGIT bound to the immunoglobulin domain of nectin-2 that is most distal from the membrane with an affinity of 6 μm, which was moderately lower than the affinity observed for the TIGIT/necl-5 interaction (3.2 μm). The TIGIT/nectin-2 binding disrupted pre-assembled nectin-2 oligomers, suggesting that receptor-ligand and ligand-ligand associations are mutually exclusive events. Indeed, the crystal structure of TIGIT bound to the first immunoglobulin domain of nectin-2 indicated that the receptor and ligand dock using the same molecular surface and a conserved "lock and key" binding motifs previously observed to mediate nectin/nectin homotypic interactions as well as TIGIT/necl-5 recognition. Using a mutagenesis approach, we dissected the energetic basis for the TIGIT/nectin-2 interaction and revealed that an "aromatic key" of nectin-2 is critical for this interaction, whereas variations in the lock were tolerated. Moreover, we found that the C-C' loop of the ligand dictates the TIGIT binding hierarchy. Altogether, these findings broaden our understanding of nectin/nectin receptor interactions and have implications for better understanding the molecular basis for autoimmune disease and cancer.
T细胞免疫球蛋白和免疫酪氨酸抑制基序结构域（TIGIT）是一种在自然杀伤（NK）细胞表面表达的抑制性受体。TIGIT识别nectin和nectin样黏附分子，因此在对恶性转化的先天免疫反应中起关键作用。尽管TIGIT与nectin样蛋白-5（necl-5）的相互作用已得到充分了解，但TIGIT如何与nectin-2结合（nectin-2是一种在乳腺癌和卵巢癌中广泛过度表达的受体）仍不清楚。在这里，我们表明TIGIT与nectin-2距膜最远的免疫球蛋白结构域结合，亲和力为6μm，略低于TIGIT/necl-5相互作用所观察到的亲和力（3.2μm）。TIGIT/nectin-2结合破坏了预先组装的nectin-2寡聚体，这表明受体-配体和配体-配体结合是相互排斥的事件。事实上，TIGIT与nectin-2第一个免疫球蛋白结构域结合的晶体结构表明，受体和配体利用相同的分子表面对接，并且使用先前观察到的保守“锁钥”结合基序来介导nectin/nectin同型相互作用以及TIGIT/necl-5识别。通过诱变方法，我们剖析了TIGIT/nectin-2相互作用的能量基础，并揭示nectin-2的“芳香族键”对这种相互作用至关重要，而“锁”的变化是可以耐受的。此外，我们发现配体的C-C'环决定了TIGIT的结合层次。总之，这些发现拓宽了我们对nectin/nectin受体相互作用的理解，并对更好地理解自身免疫性疾病和癌症的分子基础具有启示意义。
